Method, system, mobile terminal and computer program product

ABSTRACT

Systems, methods, and computer program products are provided for calculating an indicator of a quality of communication within a wireless communication access network and for estimating the available capacity of a base station within the wireless communication access network. In one exemplary embodiment, a method comprises receiving an indication, generated by a mobile terminal, of the quality of communication between the base station and the mobile terminal, and estimating the available capacity of the base station based on the received indication.

BACKGROUND

1. Technical Field

The present invention relates to a method, a system, a mobile terminaland a computer program product.

2. Description of the Related Art

In Japan, a 3G mobile phone service called Third Generation was startedin 2002. At first, exchange of small packets such as voice and mail wasthe main application. However, with the introduction of High SpeedDownlink Packet Access (HSDPA) and the like, download of larger packets,such as download of a music file or watching of a shared video, has cometo be performed.

Furthermore, since a communication infrastructure can be structuredcheaply and also since a user preference is shifting to packettransmission, shift to IP core network using IP Multimedia Subsystem(IMS) is taking place.

However, although it is a well-known fact that a fixed network typifiedby the Internet has grown into a communication infrastructureindispensable to life, there are many issues relating to ensuring ofsecurity, stable Quality of Service (QoS), and the like. Thus, NextGeneration Network (NGN) aims to ensure security and stable QoS byintroducing IMS standardized by the Third Generation Partnership Project(3GPP). Furthermore, realization of Fixed Mobile Convergence (FMC) whichuses the same IMS method and which enables to seamlessly use a mobilenetwork and a fixed network is anticipated.

Furthermore, in recent years, a mobile phone with Global PositioningSystem (GPS) has become widespread. Also, a mobile phone compliant witha plurality of wireless access methods and the introduction of amechanism allowing a user to select a wireless access method inaccordance with his/her preference are desired in the future.Additionally, JP-A-2008-298484 discloses a mobile terminal with GPS.

A user preference includes preference relating to communication cost andpreference relating to communication speed. For example, there may be auser who prefers high communication speed to low communication cost anda user who prefers low communication cost to high communication speed.The communication speed here is dependent on a wireless status(available wireless capacity) of a user. Accordingly, a technology ofgrasping the wireless status changing every moment becomes important.

In light of the foregoing, it is desirable to provide a method, asystem, a mobile terminal and a computer program product which are noveland improved, and which are for grasping the wireless status of thewireless communication device.

SUMMARY

In one embodiment, a method is provided for estimating an availablecapacity of a base station within a wireless communication accessnetwork. The method comprises receiving an indication, generated by amobile terminal, of the quality of communication between the basestation and the mobile terminal, and estimating the available capacityof the base station based on the received indication.

In another embodiment, a system is provided for estimating an availablecapacity of a base station within a wireless communication accessnetwork. The system comprises a communication unit for receiving anindication, generated by a mobile terminal, of the quality ofcommunication between the base station and the mobile terminal, and acapacity estimation unit for estimating the available capacity of thebase station based on the received indication.

In another embodiment, a mobile terminal comprises a correlationdetection unit for calculating a correlation output based on signalsreceived by the mobile terminal, an indicator calculation unit forcalculating, using the correlation output, an indication of the qualityof communication between a base station and the mobile terminal, and acommunication unit for transmitting, to the base station, the indicationof the quality of communication is provided.

In another embodiment, a method is provided for estimating an availablecapacity of a base station within a wireless communication accessnetwork. The method comprises receiving correlation outputs, generatedby a mobile terminal, of a plurality of scrambling codes forming aspecific scrambling code group, calculating, based on the receivedcorrelation outputs, an indication of the quality of communicationbetween the base station and the mobile terminal, and estimating theavailable capacity of the base station based on the calculatedindication of the quality of communication.

In another embodiment, a tangible computer-readable medium is provided.The computer-readable medium includes program instructions forperforming, when executed by a processor, a method comprisingcalculating a correlation output based on signals received by a mobileterminal, calculating, using the correlation output, an indication ofthe quality of communication between a base station and the mobileterminal, and transmitting, to the base station, the indication of thequality of communication.

In another embodiment, a mobile terminal comprises a subcarrier ratedetection unit for calculating an indication of the quality ofcommunication between a base station and the mobile terminal using adetected ratio of a number of subcarriers not used as a communicationresource among a total number of subcarriers available as acommunication resource, and a communication unit for transmitting, tothe base station, the indication of the quality of communication isprovided.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as described. Further featuresand/or variations may be provided in addition to those set forth herein.For example, the present invention may be directed to variouscombinations and subcombinations of several further features disclosedbelow in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram showing a first configuration exampleof a wireless communication system;

FIG. 2 is an explanatory diagram showing a second configuration exampleof the wireless communication system;

FIG. 3 is an explanatory diagram showing a third configuration exampleof the wireless communication system;

FIG. 4 is a block diagram showing a hardware configuration of a mobileterminal;

FIG. 5 is a functional block diagram showing a mobile terminal accordingto a first configuration example;

FIG. 6 is a functional block diagram showing a mobile terminal accordingto a second configuration example;

FIG. 7 is a functional block diagram showing a mobile terminal accordingto a third configuration example;

FIG. 8 is a functional block diagram showing a mobile terminal accordingto a fourth configuration example;

FIG. 9 is a functional block diagram showing a mobile terminal accordingto a fifth configuration example;

FIG. 10 is a flow chart showing a flow of a wireless communicationmethod performed by a mobile terminal;

FIG. 11 is an explanatory diagram showing a configuration of anestimation server;

FIG. 12 is a diagram for illustrating a method of identifying a currentlocation based on a reception intensity from each of a plurality of basestations;

FIG. 13 is a flow chart showing a first operation example of theestimation server,

FIG. 14 is a flow chart showing a second operation example of theestimation server;

FIG. 15 is a flow chart showing a third operation example of theestimation server; and

FIG. 16 is a flow chart showing a fourth operation example of theestimation server.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Additionally, in this specification and drawings, a plurality ofstructural elements having substantially the same functionalconfiguration are sometimes distinguished from each other by a differentalphabet letter added to a same numeral. For example, a plurality ofstructures having substantially the same functional configuration aredistinguished from each other as necessary by being referred to as basestations 30A, 30B and 30C. However, in case it is not necessary todistinguish between a plurality of structural elements havingsubstantially the same functional configuration, only a same numeral isadded thereto. For example, in case it is not particularly necessary todistinguish between the base stations 30A, 30B and 30C, they will becollectively referred to as the base stations 30.

Furthermore, “DETAILED DESCRIPTION OF THE EMBODIMENTS” will be describedin the order shown below.

1. Configuration of Wireless Communication System

-   -   1-1. First Configuration Example    -   1-2. Second Configuration Example    -   1-3. Third Configuration Example

2. Hardware Configuration of Mobile Terminal

3. Functional Configuration of Mobile Terminal

-   -   3-1. First Configuration Example    -   3-2. Second Configuration Example    -   3-3. Third Configuration Example    -   3-4. Fourth Configuration Example    -   3-5. Fifth Configuration Example

4. Operation of Mobile Terminal

5. Configuration of Estimation Server

6. Operation of Estimation Server

-   -   6-1. First Operation Example    -   6-2. Second Operation Example    -   6-3. Third Operation Example    -   6-4. Fourth Operation Example

7. Conclusion

1. CONFIGURATION OF WIRELESS COMMUNICATION SYSTEM

First, referring to FIGS. 1 to 3, first to third configuration examplesof a wireless communication system, which is an embodiment of thepresent invention, will be described.

1-1. First Configuration Example

FIG. 1 is an explanatory diagram showing a wireless communication system1 of a first configuration example. As shown in FIG. 1, the wirelesscommunication system 1 according to the first configuration exampleincludes an estimation server 10, a mobile terminal 20, a plurality ofbase stations 30A to 30C, and an access network 40.

The access network 40 includes a core network of a telecommunicationscarrier, and a line connecting the core network and the base station 30.The base station 30 can communicate with the estimation server 10 via agateway 42 included in the access network 40.

The base station 30 controls the communication by the mobile terminal20. For example, the base station 30 relays data received from themobile terminal 20 to an addressed destination, and when data addressedto the mobile terminal 20 is received, transmits the data to the mobileterminal 20. Furthermore, the base station 30 can communicate with themobile terminal 20 by using wireless multiple access such as frequencydivision multiple access (FDMA), time division multiple access (TDMA),and code division multiple access (CDMA). The code division multipleaccess will be briefly described in the following.

According to the code division multiple access, 512 types of scramblingcodes are defined, and any of the scrambling codes is assigned to eachbase station 30. The base station 30 frequency-spreads a transmissionsignal by a spreading code (for example, a channelization code) inaccordance with the type of the transmission signal or the mobileterminal 20, and further frequency-spreads the transmission signal byusing the assigned scrambling code and transmits the same. Additionally,the type of the transmission signal may be a common pilot channel(CPICH), a primary common control physical channel (P-CCPCH), adedicated physical channel (DPCH), a synchronization channel (SCH), orthe like.

Furthermore, the SCH includes a primary SCH and a secondary SCH. Theprimary SCH and the secondary SCH are arranged at the beginning portionof each of 15 slots configuring one frame, and the primary SCH is spreadby a C_(PSC) (Primary Synchronization Code) and the secondary SCH isspread by a C_(SSC) (Secondary Synchronization Code).

There are 16 types of C_(SSC), and 64 combination patterns are preparedto be assigned to the 15 slots. Each base station 30 is assigned withany of the 64 patterns, and the base station 30 frequency-spreads andtransmits the secondary SCH in each slot according to the assignedpattern. Additionally, the 512 types of scrambling codes are dividedinto 64 groups, and each group is associated with any of the 64 C_(SSC)combination patterns.

The mobile terminal 20 can communicate various data with other devicevia the base station 30. The various data may be audio data such asmusic, a lecture, a radio program, or the like, image data such as amotion picture, a television program, a video program, a photograph, adocument, a painting, a diagram, or the like, a game, software, or thelike.

Furthermore, in case of the mobile terminal 20 communicating with thebase station 30A as shown in FIG. 1, the mobile terminal 20 calculatesan indicator of a quality of communication, the value of which can beused by the estimation server 10, along with location identificationinformation for identifying the current location of the mobile terminal20, to generate an estimate of available capacity of the base station30A. The detailed function of such mobile terminal 20 will be describedin “3. Functional Configuration of Mobile Terminal.”

Additionally, although the mobile terminal 20 is shown as an example ofa wireless communication device in FIG. 1, the wireless communicationdevice is not limited to such example. For example, the wirelesscommunication device may be an information processing apparatus such asa personal computer (PC), a home video processing device (a DVDrecorder, a video cassette recorder, or the like), a personal digitalassistant (PDA), a home game machine, a home appliance, or the like.Also, the wireless communication device may be an information processingapparatus such as a mobile phone, a Personal Handyphone System (PHS), aportable audio playback device, a portable video processing device, aportable game machine, or the like.

The estimation server 10 receives the indicator of the quality ofcommunication and the location identification information from themobile terminal 20 via the base station 30 and the gateway 42. Theestimation server 10 can estimate the available capacity of the basestation 30 by using the indicator of the quality of communication andthe location identification information that are received. The detailedconfiguration and operation of such estimation server 10 will bedescribed later.

1-2. Second Configuration Example

FIG. 2 is an explanatory diagram showing a wireless communication system2 of a second configuration example. As shown in FIG. 2, the wirelesscommunication system 2 according to the second configuration exampleincludes the estimation server 10, the mobile terminal 20, a pluralityof first base stations 30A and 30B, a first access network 40, aplurality of second base stations 50A and 50B, and a second accessnetwork 60.

The first base station 30 is connected with the first access network 40,and the second base station 50 is connected with the second accessnetwork 60. Also, the estimation server 10 is connected with the firstaccess network 40 via a gateway 42 arranged in a core network to whichthe first base station 30 belongs, and is connected with the secondaccess network 60 via a gateway 62 arranged in a core network to whichthe second base station 50 belongs.

This wireless communication system 2 according to the secondconfiguration example allows the mobile terminal 20 to register locationwith the first base station 30A and the second base station 50Abelonging to different core networks. Accordingly, the mobile terminal20 can transmit the indicator of the quality of communication and thelocation identification information to the estimation server 10 via thegateway 42 or the gateway 62.

The estimation server 10 estimates the available capacity of the firstbase station 30A and the available capacity of the second base station50A by using the indicator of the quality of communication and thelocation identification information that are received. Furthermore, aswill be described in detail later, the estimation server 10 can selectwhich of the first access network 40 and the second access network 60 issuitably used for the mobile terminal 20.

1-3. Third Configuration Example

FIG. 3 is an explanatory diagram showing a wireless communication system3 of a third configuration example. As shown in FIG. 3, the wirelesscommunication system 3 according to the third configuration example isconfigured based on the IMS. Specifically, the wireless communicationsystem 3 according to the third configuration example includes themobile terminal 20, a plurality of base stations 30A to 30C, the accessnetwork 40, a proxy-call session control function (P-CSCF) 72, aninterrogating-CSCF (I-CSCF) 74, a serving-CSCF (S-CSCF) 75, a homesubscriber server (HSS) 76, and an application server (AS) 78.

This wireless communication system 3 according to the thirdconfiguration example allows the mobile terminal 20 to performcommunication via the base station 30 according to the IMS. Furthermore,according to the wireless communication system 3, the S-CSCF 75, the HSS76 and the AS 78, for example, function as the estimation server 10.

2. HARDWARE CONFIGURATION OF MOBILE TERMINAL

Next, a hardware configuration of the mobile terminal 20 will bedescribed with reference to FIG. 4.

FIG. 4 is a block diagram showing the hardware configuration of themobile terminal 20. The mobile terminal 20 includes a central processingunit (CPU) 201, a read only memory (ROM) 202, a random access memory(RAM) 203, and a host bus 204. Furthermore, the mobile terminal 20includes a bridge 205, an external bus 206, an interface 207, an inputdevice 208, an output device 210, a storage device (HDD) 211, a drive212, and a communication device 215.

The CPU 201 functions as an arithmetic processing device and a controldevice, and controls the entire operations of the mobile terminal 20according to various programs. Furthermore, the CPU 201 may be amicroprocessor. The ROM 202 stores programs, arithmetic parameters orthe like to be used by the CPU 201. The RAM 203 temporarily stores aprogram to be used by the CPU 201 in its execution, parameters thatchange appropriately in the execution, or the like. These areinterconnected through the host bus 204 configured from a CPU bus or thelike.

The host bus 204 is connected to the external bus 206 such as aperipheral component interconnect/interface (PCI) bus through the bridge205. Moreover, the host bus 204, the bridge 205 and the external bus 206do not necessarily have to be configured separately, and the functionsmay be implemented in a single bus.

The input device 208 is configured from input means to be used by a userto input information, such as a mouse, a keyboard, a touch panel, abutton, a microphone, a switch or a lever, an input control circuit thatgenerates an input signal based on the input by the user and outputs theinput signal to the CPU 201, and the like. The user of the mobileterminal 20 can input various types of data to the mobile terminal 20 orissue an instruction for a processing operation by operating this inputdevice 208.

The output device 210 includes, for example, a display device such as aliquid crystal display (LCD) device, an organic light emitting diode(OLED) device, or a lamp. Furthermore, the output device 210 includes anaudio output device such as a speaker, a head phone, or the like. Theoutput device 210 outputs reproduced content, for example. Specifically,the display device displays various types of information of reproducedimage data or the like in the form of text or image. For its part, theaudio output device converts reproduced audio data or the like to soundand outputs the sound.

The storage device 211 is a data storage device configured as an exampleof a storage unit of the mobile terminal 20. The storage device 211 mayinclude a storage medium, a recording device for recording data on thestorage medium, a read device for reading data out of the storagemedium, a deletion device for deleting data recorded on the storagemedium, or the like. The storage device 211 is configured from a harddisk drive (HDD), for example. The storage device 211 drives a harddisk, and stores programs to be executed by the CPU201 and various typesof data.

The drive 212 is a reader/writer for the storage medium, and is built inor externally attached to the mobile terminal 20. The drive 212 readsout information stored in an attached removable recording medium 24 suchas a magnetic disk, an optical disk, a magneto-optical disk, asemiconductor memory or the like, and outputs the information to the RAM203.

The communication device 215 is an interface for communicating with theoutside, for example. The communication device 215 may include afunction of communicating with the base station 30 and a function ofcommunicating with a GPS.

3. FUNCTIONAL CONFIGURATION OF MOBILE TERMINAL

Next, a mobile terminal 20-1 according to a first configuration examplewill be described with reference to FIG. 5, a mobile terminal 20-2according to a second configuration example will be described withreference to FIG. 6, a mobile terminal 20-3 according to a thirdconfiguration example will be described with reference to FIG. 7, amobile terminal 20-4 according to a fourth configuration example will bedescribed with reference to FIG. 8, and a mobile terminal 20-5 accordingto a fifth configuration example will be described with reference toFIG. 9.

3-1. First Configuration Example

FIG. 5 is a functional block diagram showing the mobile terminal 20-1according to the first configuration example. As shown in FIG. 5, themobile terminal 20-1 according to the first configuration exampleincludes a communication unit 220, a correlation detection unit 230 forcell search, an indicator calculation unit 240, a GPS receiving unit250, and a packet communication control unit 260. The mobile terminal20-1 according to the first configuration is applicable to the wirelesscommunication system 1 according to the first configuration example, forexample.

The communication unit 220 is an interface to the base station 30, andhas a function of a receiving unit for receiving a wireless signaltransmitted from the base station 30 and a function of a transmittingunit for transmitting a wireless signal to the base station 30.Additionally, this configuration example assumes a case where thecommunication unit 220 receives, from the base station 30, a wirelesssignal that is frequency-spread according to CDMA. Furthermore, wirelesssignals received by the communication unit 220 from k base stations 30are expressed by the following formula 1.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\\begin{matrix}{{r(t)} = {{\sum\limits_{k = 0}^{K - 1}{\sqrt{2S_{k,0}}{\xi_{k}(t)}{c_{k,0}\left( {t - \tau_{k}} \right)}{d_{k,0}\left( {t - \tau_{k}} \right)}}} +}} \\{{{\sum\limits_{k = 0}^{K - 1}{\sqrt{2S_{k,1}}{u(t)}{\xi_{k}(t)}{c_{k,1}\left( {t - \tau_{k}} \right)}{d_{k,1}\left( {t - \tau_{k}} \right)}}} +}} \\{{{\sum\limits_{k = 0}^{K - 1}{{\xi_{k}(t)}{\sum\limits_{i = 2}^{C + 1}{\sqrt{2S_{k,i}}{c_{k,i}\left( {t - \tau_{k}} \right)}{d_{k,i}\left( {t - \tau_{k}} \right)}}}}} +}} \\{{{\sum\limits_{k = 0}^{K - 1}{{\sqrt{2S_{k,1}}\begin{bmatrix}{1 -} \\{u(t)}\end{bmatrix}}{{\xi_{k}(t)}\begin{bmatrix}{{c_{psc}\left( {t - \tau} \right)} +} \\{c_{{ssc},{i{({s,m})}}}\left( {t - \tau_{k}} \right)}\end{bmatrix}}}} + {w(t)}}}\end{matrix} & \left( {{Formula}\mspace{14mu} 1} \right)\end{matrix}$

-   -   S_(k,0), c_(k,0), d_(k,0): Transmission power of CPICH,        spreading code waveform, data modulated signal waveform    -   S_(k,1), C_(d,1), d_(k,1): Transmission power of Primary-CCPCH,        spreading code waveform, data modulated signal waveform    -   S_(k,i): Transmission power of DPCH spread by an i-th        channelization code from k-th base station

The first term of the right-hand side of formula 1 indicates the CPICHsfrom the k base stations 30, the second term indicates thePrimary-CCPCHs from the k base stations, the third term indicates theDPCHs in C channels, the fourth term indicates the SCHs, and the fifthterm indicates a background noise. Furthermore, C_(k,0) is a compositespreading code, and is spread by a scrambling code C_(SC,k) and achannelization code C_(ch,0).

The correlation detection unit 230 for cell search (correlationdetection unit) can identify a scrambling code having the highestcorrelation output, i.e. the base station 30 with the smallestpropagation loss, by performing a three-step cell search based on awireless signal received by the communication unit 220. In thefollowing, the there-step cell search will be briefly described.

First, the correlation detection unit 230 for cell search detects acorrelation between a received signal and the C_(psc), and detects atiming of receiving a primary SCH (first step). Then the correlationdetection unit 230 for cell search detects a pattern having the highestcorrelation with the received signal among the 64 C_(SSC) combinationpatterns by using the timing of receiving a primary SCH detected in thefirst step (second step). As a result, a scrambling code group isidentified, and frame-based synchronization is secured. Then thecorrelation detection unit 230 for cell search detects the correlationbetween the received signal and each of 8 types of scrambling codesincluded in the identified scrambling code group, and identifies ascrambling code with the highest correlation output (third step).Additionally, the Primary-CCPCH and the DPCH are spread by a differentchannelization code, and thus they remain frequency-spread.

The indicator calculation unit 240 (calculation unit) uses thecorrelation output obtained in the process of the cell search by thecorrelation detection unit 230 for cell search to calculate an indicatorof the quality of communication for estimating the available capacity ofthe base station 30. An example of calculation by the indicatorcalculation unit 240 will be described below.

In the third step of the cell search, the CPICH, the Primary-CCPCH, andthe DPCH are detected as signals that are multiplexed while still beingspread, with regard to the correlation outputs for the other 7 types ofscrambling codes. Here, taking the ratio of the chip rate of thespreading code to the symbol rate as a spreading factor (SF), an averagevalue of 1/SF is detected as the correlation output due to thespreading.

Here, when the number of DPCHs (i.e. the number of users of the basestation 30) to be multiplexed grows, or when the number of HS-DSCHs(i.e. the number of high-speed downlink shared channels to be shared bya plurality of users in HSDPA) grows, the correlation output is greatlyincreased in spite of each DPCH or each HS-DSCH being spread, and thus,the correlation outputs for the other 7 types of scrambling codes areconsidered to become high. Similarly, when the interference from othercell grows, the interference wave from such other cell also increasesthe correlation output, and thus, the correlation outputs for the other7 types of scrambling codes are also considered to become high.Accordingly, when the correlation output for the identified scramblingcode is taken as a and the minimum value of the correlation outputs forthe other 7 types of scrambling codes is taken as b, b/a is consideredto become larger as the available capacity of the base station 30decreases due to the increase in the number of users of the base station30 or as the interference from other cell grows.

Thus, the indicator calculation unit 240 calculates the above b/a as theindicator of the quality of communication for estimating the availablecapacity. Additionally, an indicator is effective as the indicator ofthe quality of communication as long as it indicates the relationshipbetween the highest correlation output and other correlation output, andthus the indicator of the quality of communication is not limited to theabove b/a. For example, the indicator calculation unit 24 may calculatec/a as the indicator of the quality of communication, where c is anaverage value of the correlation outputs for the other 7 types ofscrambling codes.

The GPS receiving unit 250 functions as an acquisition unit foracquiring location information indicating the current location of themobile terminal 20 by receiving and decoding a GPS signal transmittedfrom a satellite. Additionally, the location information obtained by theGPS receiving unit 250 corresponds to a subordinate concept of thelocation identification information enabling the identification of alocation.

The packet communication control unit 260 transmits the indicator of thequality of communication obtained by the indicator calculation unit 240and the location identification information obtained by the GPSreceiving unit 250 to the estimation server 10 outside the core networkto which the base station 30 belongs via the gateway 42 of the corenetwork. As a result, the estimation server 10 can estimate theavailable capacity of the base station 30, for example, based on theindicator of the quality of communication and the locationidentification information.

3-2. Second Configuration Example

FIG. 6 is a functional block diagram showing a mobile terminal 20-2according to the second configuration example. As shown in FIG. 6, themobile terminal 20-2 according to the second configuration exampleincludes the communication unit 220, the correlation detection unit 230for cell search, the indicator calculation unit 240, and the packetcommunication control unit 260. The mobile terminal 20-2 according tothe second configuration is applicable the wireless communication system1 according to the first configuration example, for example.

The correlation detection unit 230 for cell search performs thethree-step cell search as with the first configuration example, and theindicator calculation unit 240 calculates the indicator of the qualityof communication based on the correlation output for each scramblingcode obtained in the process of the three-step cell search.

Furthermore, during the initial cell search and neighbouring cell searchat the time of intermittent reception, the mobile terminal 20-2 isprovided with scrambling codes of the neighbouring cells and the timingdifference by a broadcast channel (BCH) or a paging channel (PCH).

Thus, by performing correlation detection for each of scrambling codesassigned to the neighbouring cells, the correlation detection unit 230for cell search can obtain a correlation output for each of theplurality of scrambling codes as a reception intensity from each of aplurality of base stations 30.

Here, the combination of the reception intensities from the plurality ofbase stations 30 is different depending on the location of the mobileterminal 20-2. That is, since the location of the mobile terminal 20-2can be identified based on the reception intensity from each of theplurality of base stations 30, the reception intensity from each of theplurality of base stations 30 can be used as the location identificationinformation. Additionally, a concrete method of location estimationbased on the reception intensity from each of the plurality of basestations 30 will be described in “5. Configuration of EstimationServer.”

The packet communication control unit 260 transmits the indicator of thequality of communication obtained by the indicator calculation unit 240and the reception intensity from each of the plurality of base stations30 obtained by the correlation detection unit 230 for cell search as thelocation identification information to the estimation server 10 outsidethe core network to which the base stations 30 belongs via the gateway42 of the core network. As a result, the estimation server 10 canestimate the available capacity of the base stations 30, for example,based on the indicator of the quality of communication and the locationidentification information.

3-3. Third Configuration Example

Recently, Long Term Evolution (LTE) designed to increase the packettransmission/reception rate of a 3G mobile phone was developed, and theservice is planned to start around 2010. LTE employs OFDM for downlink,SC (Single Carrier)-FDM for uplink, and further employs MIMO (MultipleInput Multiple Output), and thereby achieves a maximum 100 Mbps fordownlink and maximum 50 Mbps for uplink. Accordingly, it is hoped for asa system that realizes a full-fledged high-speed wireless packetcommunication.

A mobile terminal 20-3 according to a third configuration exampledescribed below is applicable the wireless communication system 1according to the first configuration example which uses the LTEmentioned above, for example.

FIG. 7 is a functional block diagram showing the mobile terminal 20-3according to the third configuration example. As shown in FIG. 7, themobile terminal 20-3 according to the third configuration exampleincludes the communication unit 220, the GPS receiving unit 250, thepacket communication control unit 260, and an unused subcarrier ratedetection unit 270.

The communication unit 220 is an interface to the base station 30, andhas a function of a receiving unit for receiving a wireless signaltransmitted from the base station 30 and a function of a transmittingunit for transmitting a wireless signal to the base station 30.Additionally, as described above, this configuration example assumes acase where the communication unit 220 receives an OFDMA signal from thebase station 30.

As with the first configuration example, the GPS receiving unit 250functions as an acquisition unit for acquiring location informationindicating the current location of the mobile terminal 20-3 by receivingand decoding a GPS signal transmitted from a satellite. Additionally,the location information obtained by the GPS receiving unit 250corresponds to a subordinate concept of the location identificationinformation enabling the identification of a location.

The unused subcarrier rate detection unit 270 detects the ratio of thenumber of subcarriers not used as a communication resource (unusedsubcarrier rate) among the total number of subcarriers in an OFDM symbolto which a physical downlink shared channel (PDSCH) is mapped. Thefrequency of detection of the unused subcarrier rate by the unusedsubcarrier rate detection unit 270 is determined by the tradeoff betweenpower consumption and detection accuracy.

Additionally, to alleviate the issue of interference, the base station30 is assumed to make use of unused resources by nulling thesubcarriers. Accordingly, the unused subcarrier rate detection unit 270is assumed to be able to distinguish an unused resource by detectingpower of each subcarrier.

Here, the flow of basic operation by the mobile terminal 20-3 will bedescribed. The mobile terminal 20-3 can identify a physical cell IDduring the process of performing cell search for a base station 30 withthe smallest propagation loss and acquiring synchronization between aprimary synchronization signal (PSS) and a secondary synchronizationsignal (SSS).

Furthermore, the mobile terminal 20-3 obtains information such as asystem bandwidth notified by the base station 30 by decoding a physicalbroadcast channel (PBCH). Then, after performing location registrationand the like to the base station 30, the mobile terminal 20-3 startscommunication by itself or goes into an idle state (RRC_IDLE state)until a paging is received. Additionally, when in the idle state, themobile terminal 20-3 may, during the intermittent reception period,periodically search for a cell in a better condition or check whetherthere is a paging notified by a PDCCH.

Furthermore, to reselect a cell, the mobile terminal 20-3 measures thereception quality of a serving cell (an already camped cell) and aneighbouring cell. Specifically, the mobile terminal 20-3 measures thereception quality by receiving a reference signal (RS) unique to a celland obtaining the average reference signal received power. Furthermore,an indicator R-criterion is defined, and R-criteria R_(s) and R_(n) forthe serving cell and the neighbouring cell are expressed by thefollowing formulae 2 and 3.

[Equation 2]

R _(s) =Q _(meas,s) +Q _(hyst,s)  (Formula 2)

[Equation 3]

R _(n) =Q _(meas,n) +Q _(off) _(—) _(s,n)  (Formula 3)

The Q_(hyst,s)is a parameter for controlling the degree of hysteresis toprioritize the R-criteria. The Q_(off) _(—) _(s,n) is an offset amountto be applied between the serving cell and the neighbouring cell.

Next, the mobile terminal 20-3 decodes the PDCCH, which is a physicalchannel for transmitting control information, to check whether there isa paging.

The PDCCH is assigned to 3 symbols at the beginning of each subframeconfigured by 14 symbols, and the mobile terminal 20-3 in the idle statecan check whether there is a paging by decoding these 3 symbols in theintermittent period.

To efficiently decode the PDCCH, a Common search space in which a PDCCHto be transmitted to all the mobile terminals is mapped and aUE-Specific search space in which a PDCCH to be transmitted to aspecific mobile terminal is mapped are defined in the 3-symbol resourceblock. Paging information is transmitted being mapped to the Commonsearch space, and thus it is considered sufficient that an idle mobileterminal 20-3 decodes at least the Common search space.

Additionally, a cycle DRX of the intermittent reception is determined bythe mobile terminal 20-3 by processing a paging parameter notified bythe serving cell. The mobile terminal 20-3 can detect whether there isthe above-described paging and also, can reselect a cell, according tothe cycle DRX. For example, when the quality of the serving cell fallsbelow a certain threshold value, the mobile terminal 20-3 performsmeasurement of the neighbouring cell more frequently than the cycle DRX,and reduces the risk of going out of service range.

Furthermore, with regard to the measurement of the RSRP, thespecification only defines the use of the RS unique to a cell, and howmany RSs among RSs mapped in the frequency domain are to be used and howmany RSs are among RSs mapped in the time domain are to be used dependon the application.

Accordingly, the unused subcarrier rate detection unit 270 basicallyperiodically detects the unused subcarrier rate separately from themeasurement of the RSRP while taking power consumption intoconsideration. On the other hand, in case of measuring the RSRP in aregion in which a PDSCH is mapped and by using all the RSs mapped in thefrequency domain, the unused subcarrier rate detection unit 270 can alsoperform detection of the unused subcarrier rate together with the RSRPmeasurement.

The packet communication control unit 260 transmits the locationidentification information obtained by the GPS receiving unit 250 andthe unused subcarrier rate obtained by the unused subcarrier ratedetection unit 270 as the indicator of the quality of communication tothe estimation server 10 outside the core network to which the basestation 30 belongs via the gateway 42 of the core network. As a result,the estimation server 10 can estimate the available capacity of the basestation 30, for example, based on the indicator of the quality ofcommunication and the location identification information.

Additionally, if the packet communication control unit 260 is replacedby an IMS-compliant unit that functions to comply with IMS, the mobileterminal 20-3 can be applied to the wireless communication system 3according to the third configuration example shown in FIG. 3.

3-4. Fourth Configuration Example

FIG. 8 is a functional block diagram showing a mobile terminal 20-4according to a fourth configuration example. As shown in FIG. 8, themobile terminal 20-4 according to the fourth configuration exampleincludes the communication unit 220, the correlation detection unit 230for cell search, the indicator calculation unit 240, the GPS receivingunit 250, and the packet communication control unit 260. The mobileterminal 20-4 according to the fourth configuration is applicable thewireless communication system 2 according to the second configurationexample, for example.

The mobile terminal 20-4 can register location with either of the firstbase station 30 and the second base station 50. Accordingly, thecorrelation detection unit 230 for cell search and the indicatorcalculation unit 240 can acquire the indicator of the quality ofcommunication for estimating the available capacity of the first basestation 30 at the time of performing cell search for the first basestation 30, and can acquire the indicator of the quality ofcommunication for estimating the available capacity of the second basestation 50 at the time of performing cell search for the second basestation 50.

As with the first configuration example, the GPS receiving unit 250functions as an acquisition unit for acquiring location information(location identification information) indicating the current location ofthe mobile terminal 20-4 by receiving and decoding a GPS signaltransmitted from a satellite.

The packet communication control unit 260 transmits the locationidentification information obtained by the GPS receiving unit 250 andthe indicator of the quality of communication for estimating theavailable capacity of the first base station 30 obtained by theindicator calculation unit 240 to the estimation server 10 via thegateway 42 of the core network to which the base station 30 belongs.Similarly, the packet communication control unit 260 transmits thelocation identification information obtained by the GPS receiving unit250 and the indicator of the quality of communication for estimating theavailable capacity of the second base station 50 obtained by theindicator calculation unit 240 to the estimation server 10 via thegateway 62 of the core network to which the base station 50 belongs. Asa result, the estimation server 10 can estimate the available capacityof both the base station 30 and the base station 50 based on theindicator of the quality of communication and the locationidentification information.

3-5. Fifth Configuration Example

FIG. 9 is a functional block diagram showing a mobile terminal 20-5according to a fifth configuration example. As shown in FIG. 9, themobile terminal 20-5 according to the fifth configuration exampleincludes the communication unit 220, the correlation detection unit 230for cell search, the indicator calculation unit 240, the GPS receivingunit 250, and an IMS-compliant unit 280. The mobile terminal 20-5according to the fifth configuration is applicable the wirelesscommunication system 3 according to the third configuration example, forexample.

The correlation detection unit 230 for cell search performs thethree-step cell search as with the first configuration example, and theindicator calculation unit 240 calculates the indicator of the qualityof communication based on the correlation output for each scramblingcode obtained in the process of the three-step cell search.

As with the first configuration example, the GPS receiving unit 250functions as an acquisition unit for acquiring location information(location identification information) indicating the current location ofthe mobile terminal 20-5 by receiving and decoding a GPS signaltransmitted from a satellite.

The IMS-compliant unit 280 controls communication by SIP message, forexample. According to the IMS, a control communication network and amedia communication network are completely separated, and, after IMSauthentication, a radio resource is allocated at all times to thecontrol communication network for exchanging SIP messages. That is,according to the IMS, a SIP message reaches the S-CSCF 75 from themobile terminal 20-5 with high reliability. Also, a plurality of varioustypes of message bodies, such as a message in a text format, can beincluded in the SIP message.

Accordingly, the IMS-compliant unit 280 may add to the message body ofthe SIP message the location identification information obtained by theGPS receiving unit 250 and the indicator of the quality of communicationobtained by the indicator calculation unit 240. Then, the IMS-compliantunit 280 can transmit the SIP message to the S-CSCF 75, the HSS 76 orthe AS 78 on the home network side via the base station 30 and theP-CSCF 72. Additionally, the IMS-compliant unit 280 may also encrypt thelocation identification information and the indicator of the quality ofcommunication and add the same to the message body of the SIP message.

4. OPERATION OF MOBILE TERMINAL

Heretofore, configuration examples of the mobile terminal 20 have beendescribed with reference to FIGS. 5 to 9. Subsequently, the flow of awireless communication method to be performed by the mobile terminal 20will be described with reference to FIG. 10.

FIG. 10 is a flow chart showing a flow of a wireless communicationmethod performed by the mobile terminal 20. As shown in FIG. 10, thecommunication unit 220 receives a wireless signal from the base station30 (S282), and the correlation detection unit 230 for cell searchperforms the three-step cell search based on the wireless signalreceived by the communication unit 220 (S284).

Then, the indicator calculation unit 240 calculates the indicator of thequality of communication for estimating the available capacity of thebase station 30, based on the size of the correlation outputs of aplurality of scrambling codes obtained in the process of the three-stepcell search (S286). For its part, the GPS receiving unit 250 acquiresthe location information (location identification information)indicating the current location of the mobile terminal 20 by receivingand decoding a GPS signal transmitted from a satellite (S288).

The packet communication control unit 280 transmits the indicator of thequality of communication obtained by the indicator calculation unit 240and the location identification information obtained by the GPSreceiving unit 250 in this manner to the estimation server 10 via thecommunication unit 220 (S290).

5. CONFIGURATION OF ESTIMATION SERVER

Next, the configuration of the estimation server 10 will be describedwith reference to FIGS. 11 and 12.

FIG. 11 is an explanatory diagram showing the configuration of theestimation server 10. As shown in FIG. 11, the estimation server 10includes a communication unit 110, a primary available capacityestimation unit 120, a location identification unit 130, an availablecapacity correction unit 140, a storage unit 150, and an access networkselection unit 160. This estimation server 10 is applicable the first tothird configuration examples of the wireless communication system shownin FIGS. 1 to 3.

The communication unit 110 is an interface to the mobile terminal 20,and functions as a receiving unit for receiving the indicator of thequality of communication, the location identification information andthe like transmitted from the mobile terminal 20, for example, via theaccess network 40.

The primary available capacity estimation unit 120 (estimation unit)primarily estimates, from the indicator of the quality of communicationreceived by the communication unit 110, the available capacity of a cell(base station 30) with which the location of the mobile terminal 20 isregistered. For example, when the indicator of the quality ofcommunication is the b/a described above, the indicator of the qualityof communication grows larger as the number of multiplexed DPCHs, whichare channels allocated to other mobile terminals, increases.Accordingly, the primary available capacity estimation unit 120 canprimarily estimate the available capacity of the base station 30 basedon the indicator of the quality of communication b/a. More specifically,the primary available capacity estimation unit 120 may estimate theavailable capacity of the base station 30 to be at a level that ishigher as the indicator of the quality of communication b/a is smaller(the available capacity is higher), among a plurality of digital levels.

Additionally, the indicator of the quality of communication b/a isexpected to be a constant value which is not dependent on the distancebetween the base station 30 and the mobile terminal 20-1. For example,in case an AGC is not operating in a receiving circuit, each of thecorrelation outputs a and b will have a smaller value as the distancebetween the base station 30 and the mobile terminal 20-1 becomesgreater. However, the values will become smaller at the same rate, andthus, the indicator of the quality of communication b/a is assumed to beconstant, without being dependent on the distance between the basestation 30 and the mobile terminal 20-1. On the other hand, in case theAGC is operating in the receiving circuit, if the base station 30 istransmitting the same signal, the correlation outputs a and b ideallybecome constant, and thus, the indicator of the quality of communicationb/a will also be a constant value.

Furthermore, the influence of noise floor of the receiving circuit ofthe mobile terminal 20-1 on the available capacity of the base station30 that is to be estimated based on the indicator of the quality ofcommunication b/a is different depending on the distance between themobile terminal 20-1 and the base station 30. Specifically, as themobile terminal 20-1 gets farther away from the base station 30, theavailable capacity of the base station 30 will be estimated to be lessthan the actual available capacity due to the noise floor of thereceiving circuit. This is because, since the noise floor of thereceiving circuit is a random signal, the noise floor acts to increasethe value of b as the mobile terminal 20-1 gets farther away from thebase station 30. However, the communication environment of the mobileterminal 20-1 existing at the cell edge far from the base station 30 issignificantly poor, and thus, it is assumed that, even if the availablecapacity of the base station 30 is estimated to be less than the actualavailable capacity, the bad influence is restrictive.

The location identification unit 130 identifies the current location ofthe mobile terminal 20 based on the location identification informationreceived by the communication unit 110. For example, when the locationidentification information is the reception intensity from each of theplurality of base stations 30 described in “3-2. Second ConfigurationExample,” the location identification unit 130 identifies the currentlocation of the mobile terminal 20 by the method described below.

FIG. 12 is a diagram for illustrating the method of identifying thecurrent location based on the reception intensity from each of theplurality of base stations 30. Additionally, for the sake ofexplanation, the concept of a sector is not included. As shown in FIG.12, the transmission power and the absolute gain of the transmissionantenna of the base station 30A are respectively referred to as W_(A)and G_(A), the transmission power and the absolute gain of thetransmission antenna of the base station 30B are respectively referredto as W_(B) and G_(B), and the transmission power and the absolute gainof the transmission antenna of the base station 30C are respectivelyreferred to as W_(C) and G_(C).

Also, the coordinates of the base stations 30A to 30C are known, and thecoordinate of the base station 30A is A(0, 0), the coordinate of thebase station 30B is B(a, b), the coordinate of the base station 30C isC(c, d), and the coordinate at which the mobile terminal 20 is locatedis X(x, y). Also, it is assumed that the ratio of distances from pointA, point B and point C to point X is known. Furthermore, when taking thedistance from point A to point X as variable z, the ratio of the squareof the distance between point B and point X to z² as α, and the ratio ofthe square of the distance between point C and point X to z² as β, thefollowing formulae 4 to 6 are obtained.

[Equation 4]

x ² +y ² =z ²  (Formula 4)

[Equation 5]

(x−a)²+(y−b)² =αz ²  (Formula 5)

[Equation 6]

(x−c)²+(y−d)² =βz ²  (Formula 6)

Here, a, b, c, d, α (>1), and β (>1) are known values, and x, y, and zare variables. The following formula 7 is obtained from the formulae 4and 5, and the following formula 8 is obtained from the formulae 5 and6.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack & \; \\{{\left( {x - \frac{a}{1 - \alpha}} \right)^{2} + \left( {y - \frac{b}{1 - \alpha}} \right)^{2}} = {\left( {\frac{1}{\left( {1 - \alpha} \right)^{2}} - \frac{1}{1 - \alpha}} \right) \cdot \left( {a^{2} + b^{2}} \right)}} & \left( {{Formula}\mspace{14mu} 7} \right) \\\left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack & \; \\{{\left( {x - \frac{c}{1 - \beta}} \right)^{2} + \left( {y - \frac{d}{1 - \beta}} \right)^{2}} = {\left( {\frac{1}{\left( {1 - \beta} \right)^{2}} - \frac{1}{1 - \beta}} \right) \cdot \left( {c^{2} + d^{2}} \right)}} & \left( {{Formula}\mspace{14mu} 8} \right)\end{matrix}$

The formula 7 indicates the locus of a circle whose centre is (a/(1−α),b/(1=α)) and whose radius is a square root of the right-hand side.Similarly, the formula 8 indicates the locus of a circle whose centre is(c/(1−β), d(1−β)) and whose radius is a square root of the right-handside. Accordingly, (x, y) satisfying the formulae 4 to 6 corresponds tothe intersection of the loci of the two circles indicated by theformulae 7 and 8.

On the other hand, received power densities P_(A), P_(B), and P_(C) fromthe base stations 30A, 30B and 30C at X(x, y) are expressed by thefollowing formulae 9 to 11.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack & \; \\{P_{A} = \frac{W_{A}G_{A}}{4\pi \; d^{2}}} & \left( {{Formula}\mspace{14mu} 9} \right) \\\left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack & \; \\{P_{B} = \frac{W_{B}G_{B}}{4{\pi\alpha}\; d^{2}}} & \left( {{Formula}\mspace{14mu} 10} \right) \\\left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack & \; \\{P_{C} = \frac{W_{C}G_{C}}{4{\pi\beta}\; d^{2}}} & \left( {{Formula}\mspace{14mu} 11} \right)\end{matrix}$

When W_(A)=W_(B)=W_(C) and G_(A)=G_(B)=G_(C), the following formulae 12and 13 are obtained from the formulae 9 to 11.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack & \; \\{\alpha = \frac{P_{A}}{P_{B}}} & \left( {{Formula}\mspace{14mu} 12} \right) \\\left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack & \; \\{\beta = \frac{P_{A}}{P_{C}}} & \left( {{Formula}\mspace{14mu} 13} \right)\end{matrix}$

The α and β will be known values by the above formulae 12 and 13.Additionally, even if the transmission outputs W_(A), W_(B) and W_(C) ofthe base stations 30A to 30C are different, the ratio of distances fromrespective base stations 30 to X(x, y) can be obtained, provided thatinformation relating to the transmission outputs of the base stations30A to 30C is notified by the BCH. The same can be said for a case wherethe transmission output of the CPICH is notified by the BCH.

The location identification unit 130 can identify the current locationof the mobile terminal 20 from the reception intensity, as the locationidentification information, from each of the plurality of base stations30 by the above calculations. Additionally, when the locationidentification information is location information indicating latitudeand longitude, the location identification unit 130 does not have toperform any special calculation.

We will return to the description of the configuration of the estimationserver 10 with reference to FIG. 11. As has been described, the primaryavailable capacity estimation unit 120 estimates the available capacityof the base station 30 based on, for example, the indicator of thequality of communication b/a. However, as the mobile terminal 20 getsfarther away from the base station 30, the base station 30 will set theamplitude of the DPCH allocated to the mobile terminal 20 to be larger,and thus the value of b will become larger. That is, the indicator ofthe quality of communication b/a will have a different meaning withregard to the available capacity of the base station 30 depending on thelocation of the mobile terminal 20.

In the following, the influence of the distance between the mobileterminal 20 and the base station 30 on the available capacity of thebase station 30 that is estimated based on the indicator of the qualityof communication b/a will be described in greater detail. Let us assumethat the estimation server 10 has estimated the available capacity ofthe base station 30 based on an indicator of the quality ofcommunication b1/a1 received from the mobile terminal 20 that isattempting to start communication. Here, in case the mobile terminal 20exists near the base station 30, the base station 30 canmultiple-transmit a DPCH for the mobile terminal 20 with low power.Accordingly, the influence on the available capacity (degree ofcongestion) of the base station 30 due to the start of signaltransmission to this mobile terminal 20 existing near the base station30 is small. That is, the amount of reduction in the available capacityof the base station 30 caused by the start of signal transmission to themobile terminal 20 existing near the base station 30 is small.

On the other hand, in case the mobile terminal 20 exists far from thebase station 30, the base station 30 will multiple-transmit a DPCH forthis mobile terminal 20 with high power. Accordingly, the influence onthe available capacity (degree of congestion) of the base station 30 dueto the start of signal transmission to this mobile terminal 20 existingfar from the base station 30 is large. That is, the amount of reductionin the available capacity of the base station 30 caused by the start ofsignal transmission to the mobile terminal 20 existing far from the basestation 30 is large.

Thus, the available capacity correction unit 140 (correction unit)corrects the available capacity of the base station 30 estimated by theprimary available capacity estimation unit 120 by using the distancebetween the mobile terminal 20 and the base station 30. Specifically,the available capacity correction unit 140 may correct the availablecapacity of the base station 30 estimated by the primary availablecapacity estimation unit 120 to a value smaller as the distance betweenthe mobile terminal 20 and the base station 30 is increased.Additionally, the distance between the mobile terminal 20 and the basestation 30 can be obtained from the difference between the location ofthe mobile terminal 20 identified by the location identification unit130 and the known installation location of the base station 30.

The storage unit 150 is a storage medium storing user information,history information, communication cost information, available capacityinformation, and the like. Additionally, the storage unit 150 (userinformation storage unit, communication cost storage unit) may be astorage medium such as a non-volatile memory, a magnetic disk, anoptical disk, a magneto optical (MO) disk, and the like. Thenon-volatile memory may be an electrically erasable programmableread-only memory (EEPROM), and an erasable programmable ROM (EPROM), forexample. Also, the magnetic disk may be a hard disk, a discoid magneticdisk, and the like. Also, the optical disk may be a compact disc (CD), adigital versatile disc recordable (DVD-R), a Blu-ray disc (BD;registered trademark), and the like.

When a plurality of access networks can be used by the mobile terminal20 as shown in FIG. 2, the access network selection unit 160 (selectionunit) selects an access network suitable for the mobile terminal 20based on the available capacity corrected by the available capacitycorrection unit 140 and various types of information stored in thestorage unit 150. Concrete example of this selection will be describedin “6-3. Third Operation Example” and “6-4. Fourth Operation Example.”

6. OPERATION OF ESTIMATION SERVER

Heretofore, the configuration of the estimation server 10 has beendescribed with reference to FIGS. 11 and 12. Subsequently, the first tofourth configuration examples of the estimation server 10 will bedescribed with reference to FIGS. 13 to 16.

6-1. First Operation Example

FIG. 13 is a flow chart showing the first operation example of theestimation server 10. As shown in FIG. 13, first, when the communicationunit 110 of the estimation server 10 receives the indicator of thequality of communication and the location identification informationfrom the mobile terminal 20 (S310), the primary available capacityestimation unit 120 primarily estimates the available capacity of thebase station 30 based on the indicator of the quality of communication(S320). Also, when the location identification information is notinformation directly indicating the latitude and longitude, the locationidentification unit 130 identifies the current location of the mobileterminal 20 based on the location identification information (S330).Then, the available capacity correction unit 140 corrects the availablecapacity estimated by the primary available estimation unit 120 by usingthe distance between the mobile terminal 20 and the base station 30(S340).

6-2. Second Operation Example

FIG. 14 is a flow chart showing the second operation example of theestimation server 10. As shown in FIG. 14, the second operation exampleincludes, after the processes of S310 to S340 shown in the firstoperation example, a process of further correcting the availablecapacity based on history information (S350). The history information isstored in the storage unit 150, and is information relating to thehistory of influences of the location information of many mobileterminals on the available capacity, information relating to the historyof the QoSs that are actually obtained, and the like. The availablecapacity correction unit 140 further corrects, by using the historyinformation, the available capacity that has been corrected in S340 byusing the location information. Let us assume, for example, that thehistory information includes the relationship between a previouslyestimated available capacity and the QoS, and that the QoS is less thanthe QoS expected from the estimated available capacity. In this case,the actual available capacity is considered to be less than theestimated available capacity, and thus, the available capacitycorrection unit 140 may correct the available capacity to be less.

6-3. Third Operation Example

FIG. 15 is a flow chart showing the third operation example of theestimation server 10. As shown in FIG. 15, the third operation exampleincludes, after the processes of S310 to S340 shown in the firstoperation example, storing of the available capacity (S360) andselection of an access network (S370).

Specifically, the available capacity corrected by the available capacitycorrection unit 140 in S340 is stored in the storage unit 150 (S360).The storage unit 150 also stores user information indicating thepreference of a user of the mobile terminal 20 on communication.Weighting on cost indicating that a user desires low cost, weighting onhigh communication speed indicating that a user desires high-speedcommunication, and the like, are set as the user information. This userinformation may be set based on a user operation on the mobile terminal20. Furthermore, the storage unit 150 stores communication costinformation indicating the communication cost for each access network.For example, information indicating the communication cost per unittime, information indicating the communication cost per unit dataamount, and the like, are assumed as the communication cost information,for example.

Then, the access network selection unit 160 selects an access networksuitable for the user of the mobile terminal 20 based on the availablecapacity stored in the storage unit 150, the user information and thecommunication cost information (S370). For example, when preference forcost is set in the user information of the mobile terminal 20, theaccess network selection unit 160 refers to the communication costinformation, selects an access network with the lowest communicationcost, and notifies the mobile terminal 20. On the other hand, whenpreference for high communication speed is set in the user informationof the mobile terminal 20, the access network selection unit 160 refersto the available capacity for each access network stored in the storageunit 150, selects an access network with the highest available capacity,and notifies the mobile terminal 20. Additionally, preference of a usermay be set in the user information according to conditions. For example,preference for high communication speed is set in case of downloading apacket having a certain size or more, and preference for cost is set inother cases.

6-4. Fourth Operation Example

FIG. 16 is a flow chart showing the fourth operation example of theestimation server 10. As shown in FIG. 16, the fourth operation exampleincludes, after the processes of S310 to S340 shown in the firstoperation example, storing of the available capacity (S360) andselection of an access network (S380).

Specifically, the available capacity corrected by the available capacitycorrection unit 140 in S340 is stored in the storage unit 150 (S360).Furthermore, in this operation example, the communication cost isassumed to change depending on the available capacity, and the storageunit 150 stores variable cost information indicating the communicationcost per available capacity.

Then, the access network selection unit 160 selects an access networksuitable for the user of the mobile terminal 20 based on the availablecapacity stored in the storage unit 150, the user information and thevariable cost information (S380). Specifically, the access networkselection unit 160 acquires communication costs in accordance with theavailable capacities of respective access networks, and in casepreference for cost is set in the user information of the mobileterminal 20, selects an access network with the lowest communicationcost, and notifies the mobile terminal 20. On the other hand, whenpreference for high communication speed is set in the user informationof the mobile terminal 20, the access network selection unit 160 refersto the available capacity of each access network stored in the storageunit 150, selects an access network with the highest available capacity,and notifies the mobile terminal 20.

7. CONCLUSION

As has been explained, according to the embodiments of the presentinvention, the following effects can be obtained.

The estimation server 10 can estimate the available capacity of the basestation 30 with which the location of the mobile terminal 20 isregistered based on an approximate value of an relative amplitude ratio(b/a) of DPCHs allocated to other mobile terminals.

Furthermore, the estimation server 10 notifies the mobile terminal 20 ofthe estimated available capacity of the base station 30, therebyenabling the mobile terminal 20 to grasp the available capacity of thebase station 30 with which the location of the mobile terminal 20 isregistered.

Furthermore, the estimation server 10 can identify the location of themobile terminal 20 even when a GPS function is not provided to themobile terminal 20 as shown in the second configuration example or evenwhen the mobile terminal 20 is at a location where it is hard to use theGPS function.

Furthermore, the estimation server 10 can select an access network bestsuited to a user at the time, according to the preference of the user ofthe mobile terminal 20. Furthermore, even in a case of the communicationcost changing depending on the relationship between supply and demand,the estimation server 10 can select an appropriate access networkaccording to the changing communication cost.

Furthermore, by configuring the system according to IMS, as with thewireless communication system 3 according to the third configurationexample, the mobile terminal 20 is enabled to communicate with theestimation server 10 (S-CSCF 75, AS 78, and the like) by using a SIPmessage.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

For example, an example has been described above where the mobileterminal 20 calculates the indicator of the quality of communicationbased on the correlation output of a scrambling code and notifies theestimation server 10 of this indicator of the quality of communication.However, the present invention is not limited to such an example. As amodified example, the mobile terminal 20 may notify the estimationserver 10 of correlation outputs of a plurality of scrambling codesforming a specific scrambling code group, and the estimation server 10may calculate the indicator of the quality of communication based on thenotified correlation outputs and estimate the available capacity of thebase station 30 from the indicator of the quality of communication.

Furthermore, it is not necessary to perform each step in the processingof the estimation server 10 and the mobile terminal 20 in chronologicalorder according to the sequence shown in the sequence chart or the flowchart. For example, each step in the processing of the estimation server10 and the mobile terminal 20 may include the processing which isperformed in parallel or individually (e.g. parallel processing orobject processing).

Furthermore, it is also possible to create a computer program forcausing hardware such as the CPU 201, the ROM 202, and the RAM 203 thatare built in the estimation server 10 and the mobile terminal 20 toperform functions that are the same as each structural element of theestimation server 10 and the mobile terminal 20 described above. Astorage medium storing the computer program is also provided.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-126951 filedin the Japan Patent Office on May 26, 2009, the entire content of whichis hereby incorporated by reference.

1. A method for estimating an available capacity of a base stationwithin a wireless communication access network, the method comprising:receiving an indication, generated by a mobile terminal, of the qualityof communication between the base station and the mobile terminal; andestimating the available capacity of the base station based on thereceived indication.
 2. The method of claim 1, wherein the indication ofthe quality of communication is calculated using a three-step cellsearch based on a signal received by the mobile terminal and correlationoutputs of a plurality of scrambling codes.
 3. The method of claim 2,wherein the three-step cell search comprises: detecting a correlationbetween a signal received by the mobile terminal and a primarysynchronization code; detecting the timing of a received primarysynchronization channel; detecting, using the timing of the receivedprimary synchronization channel, a pattern having the highestcorrelation with the received signal among combination patterns of asynchronization code; detecting the correlation between the receivedsignal and scrambling codes included in a scrambling code group; andidentifying a scrambling code with the highest correlation output. 4.The method of claim 3, wherein a relationship between the highestcorrelation output and the correlation outputs between the receivedsignal and each of the other scrambling codes of the scrambling codegroup is the minimum value of the correlation outputs between thereceived signal and each of the other scrambling codes of the scramblingcode group divided by the correlation output for the identifiedscrambling code.
 5. The method of claim 3, wherein a relationshipbetween the highest correlation output and the correlation outputsbetween the received signal and each of the other scrambling codes ofthe scrambling code group is the average value of the correlationoutputs between the received signal and each of the other scramblingcodes of the scrambling code group divided by the correlation output forthe identified scrambling code.
 6. The method of claim 4, wherein adecrease in the relationship between the highest correlation output andthe correlation outputs between the received signal and each of theother scrambling codes of the scrambling code group indicates anincrease in the estimated available capacity of the base station.
 7. Themethod of claim 1, further comprising: receiving location informationcomprising the current location of the mobile terminal, the locationinformation being generated by the mobile terminal; and adjusting theestimated available capacity of the base station based on the locationinformation.
 8. The method of claim 1, further comprising: selecting,for the mobile terminal, a wireless communication access network basedon the estimated available capacity and user selected preferences. 9.The method of claim 1, wherein the indication of the quality ofcommunication is based on at least one of a level of interference, anunused subcarrier rate, and a power level of a received signal.
 10. Asystem for estimating an available capacity of a base station within awireless communication access network, the system comprising: acommunication unit for receiving an indication, generated by a mobileterminal, of the quality of communication between the base station andthe mobile terminal; and a capacity estimation unit for estimating theavailable capacity of the base station based on the received indication.11. The system of claim 10, further comprising: a locationidentification unit for identifying the location of the mobile terminalusing location identification information received by the system; and anavailable capacity correction unit for adjusting the estimated availablecapacity of the base station based on the identified location of themobile terminal.
 12. The system of claim 11, wherein the locationidentification information comprises an indication of the receptionintensity from a plurality of base stations located within the wirelesscommunication access network.
 13. The system of claim 11, wherein thelocation identification information comprises information generated by aGPS unit.
 14. The system of claim 10, further comprising: a storage unitfor storing user information; and an access network selection unit forselecting a wireless communication access network based on the estimatedavailable capacity and the user information.
 15. The system of claim 10,wherein the quality of communication is based on at least one of a levelof interference, an unused subcarrier rate, and a power level of areceived signal.
 16. A mobile terminal comprising: a correlationdetection unit for calculating a correlation output based on signalsreceived by the mobile terminal; an indicator calculation unit forcalculating, using the correlation output, an indication of the qualityof communication between a base station and the mobile terminal; and acommunication unit for transmitting, to the base station, the indicationof the quality of communication.
 17. The mobile terminal of claim 16,wherein calculating the correlation output comprises a three-step cellsearch comprising: detecting a correlation between a signal received bythe mobile terminal and a primary synchronization code; detecting thetiming of a received primary synchronization channel; detecting, usingthe timing of the received primary synchronization channel, a patternhaving the highest correlation with the received signal amongcombination patterns of a synchronization code; detecting thecorrelation between the received signal and scrambling codes included ina scrambling code group; and identifying a scrambling code with thehighest correlation output.
 18. The mobile terminal of claim 17, whereina relationship between the highest correlation output and thecorrelation outputs between the received signal and each of the otherscrambling codes of the scrambling code group is the minimum value ofthe correlation outputs between the received signal and each of theother scrambling codes of the scrambling code group divided by thecorrelation output for the identified scrambling code.
 19. The mobileterminal of claim 17, wherein a relationship between the highestcorrelation output and the correlation outputs between the receivedsignal and each of the other scrambling codes of the scrambling codegroup is the average value of the correlation outputs between thereceived signal and each of the other scrambling codes of the scramblingcode group divided by the correlation output for the identifiedscrambling code.
 20. The mobile terminal of claim 18, wherein a decreasein the relationship between the highest correlation output and thecorrelation outputs between the received signal and each of the otherscrambling codes of the scrambling code group indicates an increase inan estimated available capacity of the base station.
 21. The mobileterminal of claim 16, further comprising: a GPS unit for acquiringlocation information indicating the current location of the mobileterminal, wherein the location information is transmitted to the basestation.
 22. The mobile terminal of claim 16, wherein the indication ofthe quality of communication is based on at least one of a level ofinterference, an unused subcarrier rate, and a power level of a receivedsignal.
 23. A method for estimating an available capacity of a basestation within a wireless communication access network, the methodcomprising: receiving correlation outputs, generated by a mobileterminal, of a plurality of scrambling codes forming a specificscrambling code group; calculating, based on the received correlationoutputs, an indication of the quality of communication between the basestation and the mobile terminal; and estimating the available capacityof the base station based on the calculated indication of the quality ofcommunication.
 24. The method of claim 23, wherein the correlationoutputs comprise correlation values indicating a relationship between afirst scrambling code having the highest correlation output to a signalreceived by the mobile terminal and a correlation output of a secondscrambling code to the signal received by the mobile terminal.
 25. Themethod of claim 23, further comprising: receiving location information,generated by the mobile terminal, comprising the current location of themobile terminal; and adjusting the estimated available capacity of thebase station based on the location information.
 26. The method of claim23, further comprising: selecting, for the mobile terminal, a wirelesscommunication access network based on the estimated available capacityand user selected preferences.
 27. The method of claim 23, wherein thequality of communication is based on at least one of a level ofinterference, an unused subcarrier rate, and a power level of a receivedsignal.
 28. A tangible computer-readable medium including programinstructions for performing, when executed by a processor, a methodcomprising: calculating a correlation output based on signals receivedby a mobile terminal; calculating, using the correlation output, anindication of the quality of communication between a base station andthe mobile terminal; and transmitting, to the base station, theindication of the quality of communication.
 29. The tangiblecomputer-readable medium of claim 28, wherein calculating thecorrelation output comprises a three-step cell search comprising:detecting a correlation between a signal received by the mobile terminaland a primary synchronization code; detecting the timing of a receivedprimary synchronization channel; detecting, using the timing of thereceived primary synchronization channel, a pattern having the highestcorrelation with the received signal among combination patterns of asynchronization code; detecting the correlation between the receivedsignal and scrambling codes included in a scrambling code group; andidentifying a scrambling code with the highest correlation output. 30.The tangible computer-readable medium of claim 29, wherein arelationship between the highest correlation output and the correlationoutputs between the received signal and each of the other scramblingcodes of the scrambling code group is the minimum value of thecorrelation outputs between the received signal and each of the otherscrambling codes of the scrambling code group divided by the correlationoutput for the identified scrambling code.
 31. The tangiblecomputer-readable medium of claim 29, wherein a relationship between thehighest correlation output and the correlation outputs between thereceived signal and each of the other scrambling codes of the scramblingcode group is the average value of the correlation outputs between thereceived signal and each of the other scrambling codes of the scramblingcode group divided by the correlation output for the identifiedscrambling code.
 32. The tangible computer-readable medium of claim 30,wherein a decrease in the relationship between the highest correlationoutput and the correlation outputs between the received signal and eachof the other scrambling codes of the scrambling code group indicates anincrease in an estimated available capacity of the base station.
 33. Thetangible computer-readable medium of claim 28, the method furthercomprising: acquiring location information indicating the currentlocation of the mobile terminal; and transmitting the locationinformation to the base station.
 34. The tangible computer-readablemedium of claim 28, wherein the indication of the quality ofcommunication is based on at least one of a level of interference, anunused subcarrier rate, and a power level of a received signal.
 35. Amobile terminal comprising: a subcarrier rate detection unit forcalculating an indication of the quality of communication between a basestation and the mobile terminal using a detected ratio of a number ofsubcarriers not used as a communication resource among a total number ofsubcarriers available as a communication resource; and a communicationunit for transmitting, to the base station, the indication of thequality of communication.